Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$24.38	5.558%	$25.735	$25.74	$25.75	$25.70
Purchase #2	$36.52	3.475%	$37.7891	$37.79	$37.80	$37.80
Purchase #3	$209.74	4.248%	$218.6498	$218.65	$218.65	$218.60
Purchase #4	$13.86	8.242%	$15.0023	$15.00	$15.00	$15.00
Purchase #5	$185.83	12.854%	$209.7166	$209.72	$209.70	$209.70
Purchase #6	$247.46	10.504%	$273.4532	$273.45	$273.45	$273.50
Purchase #7	$82.45	9.522%	$90.3009	$90.30	$90.30	$90.30
7 purchase totals =	$800.24		$870.6469	$870.65	$870.65	$870.60